The present invention relates to homogeneous compositions used in the manufacture of rigid polyurethane and/or polyisocyanurate foams and, more particularly, foams used in areas which require a good fire resistance such as decorations, buildings, or vehicles. The object of the invention concerns homogeneous compositions of halogenated polyhydroxylated compounds and halogenated alkanes kept in the form of a microemulsion by means of a surfactant.
For the manufacture of rigid polyurethane and/or polyisocyanurate foams having a good fire resistance, it is known to use polyhydroxylated halogenated compounds having a good reactivity with respect to isocyanates. For this kind of application, one prefers polyhydroxylated compounds of low molecular weight possessing at least two hydroxyl groups per molecule, but preferably 3 or 4, and a hydroxyl value at least equal to 250, but preferably between 300 and 600. Moreover, in order to obtain rigid foams having good fire-resistant properties; i.e., oxygen limit index (LOI) values, according to standard NF 51.071, above 26 and, better still, above 28, it is recommended to use halogenated polyols having a halogen content and more particularly, a bromine content as high as possible and preferably from 35 to 45% by weight. Such compounds are described in numerous patents such as, for instance, in French Pat. Nos. 1,350,425, 2,180,138, 1,401,803, 2,229,680, as well as in U.S. Pat. No. 3,385,900. They are likewise described in the literature such as, for example, in Flame Retardancy of Polymeric Materials, vol. 3, edited by W. C. KURYLA and A. J. PAPA, concerning, in particular, the fireproofing of polyurethane foams.
These rigid foams are obtained by the reactions of at least one polyhydroxylated halogenated compound with a polyisocyanate in the presence of a foaming agent. These foaming agents are selected from the family of halogenated alkanes, generally chlorinated and/or fluorinated, containing from 1 to 3 atoms of carbon such as, for example, methylene chloride or the Freons like trichlorofluoromethane, dichlorodifluoromethane, or trichlorotrifluoromethane. The incorporation of these halogenated alkanes into the formulations for rigid foams is not easy because of their incompatibility with the mixture of the other constituents, which results in a poor emulsification of the constituents of the mixture and most often a very rapid separation of the foaming agent. This phenomenon is observed in particular in the formulations based on polyols of low molecular weight, highly halogenated and weakly oxyalkylenated, above all the weakly oxypropylenated polyols or polyols not oxypropylenated at all. With such a heterogeneous system most often involving the separation of the basic constituents and the foaming agent, it is difficult to fabricate rigid foams of good quality because of the lack of uniform distribution of the effects of each of the constituents. The technological behavior of the systems thus constituted is not satisfactory.